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In my edition of MR&A/C,published in 2000, it does describe a run capacitor on pg. 1159 of the glossary as "A device that dissipates heat generated by a motor." This is clearly in error and should have been caught by the editors. What they are trying to say is that the run cap has to be built to dissipate the heat it develops since it is left in the circuit while the motor runs, as contrasted to a start cap which is only energized for a fraction of a second and therefore doesn't have sufficient time to heat up. This is explained in the text on pg. 268.

In my edition of MR&A/C,published in 2000, it does describe a run capacitor on pg. 1159 of the glossary as "A device that dissipates heat generated by a motor." This is clearly in error and should have been caught by the editors.

Originally posted by condenseddave And, Mark, the start winding (And start capacitor) IS deenergized when a motor reaches full load.

This is only true in a couple of types of motors. In the PSC motors used in compressors and fans we see every day, the start winding is energized in parallel with the run winding whenever the motor is running.

The run capacitor is in series with the start winding.

If there is a start capacitor, it is in parallel with the run capacitor, so thier capacitance actually adds.

The start capacitor should be removed from the circuit when the motor gets to about 75-80% of its full speed. Leaving it in to long will cause the capacitor to fail because start capacitors generally have no way to get rid of the heat generated by the current flow through them.

On a PSC motor, if you check with an amp meter, you will have current through both the run and the start windings, but because the currents through the 2 windings are out of phase with eachother, run current + start current does not = current found at common. If you clamp your meter around run and start at the same time, the current will = what you find at common.

Because we have moving magnetic fiends and coils of wire, we also get a fun thing called back EMF being induced. That is the voltage you get if you check the voltage between start and run. This is the voltage you need to know when you are determining what potential relay is needed for a start kit, and determining what voltage rating you need for a capacitor.

i agree with oilman. all caps are wired IN SERIES with start winding. The reference in Mod REfrig.book is a typo. All caps generate thier own heat. run caps generate less @ are oil cooled. Start caps are of paper @ plastic construction. Designed to be used breifly, then drop out of circuit when motor gets to 75% of speed, via a current or potential relay. Anyone ever run into an exploded start cap due to a stuck closed relay? hats because it overheated.